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Linting

Linting is a
problem which has always concerned the papermaking and printing industry.In the offset printing process, loose fibres
and fines from the uncoated paper adhere to the blanket and disrupt the
transfer of ink.This reduces the print
quality and is a major effect on the pressroom efficiency.

Linting is
complex because it is a dynamic process that is influenced by both the printing
press and paper variables.The lint
particles continuously move on and off the blanket, either transferring back to
the paper or to the printing plate or into the ink and water systems – making
it difficult to measure lint reproducibly.This is why the lint measured after any printing trial from the blanket
is only part of the lint that has been removed from the surface of the
paper.

Most of the recent work
has been investigating the dynamics of lint migration during offset printing to
measure the rate of lint transfer and to gain understanding how it relates to
the paper properties and printing press variables. This work was done using a high speed video
camera combined with image analysis techniques.Figure 1 below shows the captured image of lint build-up during a press
run, while Figure 2 shows threshold results from dynamic and static images
after performing image analysis.

Figure 1.An Example of lint build-up captured by the
lint camera during a press run. (A) Dynamic images at the very beginning of
run; (B) Dynamic images at 500 copies; (C) Dynamic images at 7000 copies.Press speed was 8000 copies an hour.

Figure 2. Dynamic (top
row) and static (bottom row) images of 45gsm newsprint after printing 7000
copies at tack 12.5 acquired by the lint camera. (A) Raw image of an analysed
area; (B) Image after applying manual threshold to the dynamic and static
images in (A).Note: static images were taken at the end of run, after the press is
halted.

This is the linting research group in 2005- Left to Right are: Paul Banham
(Norske Skog), Warren Batchelor, Afriana Sudarno and Chamundi Gujjari
(Australian Pulp and Paper Institute). The photo was taken at the
Smartprint CRC annual conference in October 2005.